1. Field of the Invention
The present invention relates to a robust control for a three-position actuator piston assembly of the type utilized to control the double-acting clutches of a change-gear transmission, such as the splitter clutches or range clutches of a compound transmission. In particular, the present invention relates to a robust control for a pressurized, fluid-actuated actuator piston assembly providing three selectable, maintainable positions (axially centered, axially displaced in a first direction, and axially displaced in a second direction) and requiring only a single controllable, variable pressure fluid supply device including a pulse-width-modulated, solenoid-controlled valve.
2. Description of the Prior Art
Change-gear mechanical transmissions having double-acting clutch mechanisms, of both the synchronized and non-synchronized types, are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,335,616; 4,428,469; 4,754,665; 4,920,815; 4,944,197; 5,086,897; 5,370,013 and 5,390,561, the disclosures of which are incorporated herein by reference. Two-position and three-position, fluid-actuated, actuator piston assemblies and actuator systems associated therewith also are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,899,607; 4,928,544; 4,936,156; 5,054,591; 5,193,410; 5,263,379; 5,272,441 and 5,329,826, the disclosures of which are incorporated herein by reference.
A transmission utilizing a three-position splitter actuator and a splitter clutch having increased backlash is disclosed in U.S. Pat. No. 5,651,292, the disclosure of which is incorporated herein by reference.
A fluid pressure-operated, three-position shift actuator requiring only a single controlled source of pressurized fluid is disclosed in U.S. Pat. No. 5,661,998, the disclosure of which is incorporated herein by reference.
As described in U.S. Pat. No. 5,661,998, the three-position piston is used to achieve a mid-position or neutral state in which neither of the splitter gears is engaged. This neutral state allows the gear set that is being shifted to, to achieve a synchronized speed with the engaging member (the sliding clutch) and, as such, provides a much smoother shift.
This mid- or neutral position is obtained by applying a constant air pressure signal to the smaller piston face side of the splitter cylinder and a lower pressure to the larger piston face side. This lower pressure is achieved by pulse width modulating (PWM'ing) a solenoid valve that applies air pressure to the aft side of the piston. This PWM'ing entails rapidly turning a three-way, two-position, solenoid-controlled valve on and then off to achieve a pressure somewhere between zero psi and the full system pressure.
Testing of the prior art system has shown that the range of PWM values resulting in this neutral state is so small that it makes utilizing this method of control difficult for vehicular transmission applications. Operating variables such as temperature, voltage, pressure, contamination and manufacturing variations for both the solenoid valve and the splitter piston all play together to affect the range of PWM values that yield neutral.